The invention relates to a belt tensioner for attaching to a generator of an auxiliary unit drive of an internal combustion engine, comprising: a tensioner housing which is mounted on the generator and has a cavity, two tensioning rollers which act with a pretensioning force on the belt in its direction of revolution upstream and downstream of the belt pulley of the generator, a bow spring which produces the pretensioning force and is accommodated in the cavity, a circular-arc-shaped tensioning lever which is mounted in the cavity so as to be movable in the plane of the circular arc and which, on the one hand, is acted on by the force of the bow spring and, on the other hand, supports one of the tensioning rollers, and a sliding bearing for the tensioning lever, which sliding bearing extends at the inlet of the cavity.
Such a belt tensioner is known from DE 10 2011 082 764 A1 and DE 10 2011 084 680 B3. The belt tensioner is intended for mounting on a starter generator arranged in the auxiliary unit drive of an internal combustion engine. With its belt pulley which alternately takes up and delivers torque, i.e. in the generator mode or in the starting mode of the internal combustion engine, this tensioner brings about a corresponding change of tensioned strand and slack strand of the revolving belt. Therefore, the tensioning of the slack strand requires a belt tensioner with two tensioning rollers which pretension the belt upstream and downstream of the belt pulley. The two tensioning rollers of the belt tensioner are mounted, on the one hand, on a circular-arc-shaped tensioning lever and, on the other hand, on a tensioner housing which has a cavity, in which the tensioning lever is mounted, containing the bow spring clamped therein between the tensioning lever and the tensioner housing.